sounds like you are doing the right thing. Like the chap said above. If you have waxed up or sealed the car and you want to do it again. I find personally its best to strip off the wax thats on there already. So IPA (you can by big 5 litres of it on amazon for say 10 pounds) mixed down with water about 60% water 40% IPA will strip the wax off your car. Spray the panels down with IPA and use a nice plush cloth to work the ipa around the panel. Make sure you rinse the car down completly at the end so now IPA is left kicking around before you wax.
Ive not had problems with the finish sprays effecting the beading of the wax or sealant. I find the finishing sprays sort of top up the protection and maintain the beading (we all use beading as the kind of way to measure that your sealant and wax is still there). I noticed for sure that if you use a finishing spray you get much more shelf life from your wax or sealant. The sealant you mention colenite 845 (I think thats collenites sythetic wax aka sealant) is really good. I plan to go back to it as my main sealant but peeps keep buying me AGP for xmas birthdays etc.. cant use it quicker than I get it! but its ok.
I personally would strip all the old wax from the car before applying new protection.
The reason's are obvious if you think about it, why put fresh wax over wax that's partially degraded? It will affect the new wax's ability to bond and seriously shorten its longevity.
Use a proper product for removing your current protection, Fairy Liquid doesn't remove wax, the salts it contains just mask the wax's effects for a brief period, a product like CarPro Eraser is what you need to use. I would them carry out a full decontamination, it's always worth doing and doen't take long. When that's done wipe down with IPA (10% should be enough if you're not polishing the car) then apply the Collinite first as it has greater longevity than the .50 Cal, leave the Collinite to gas out for 8-24hrs the apply the Penta Wax.
As for quick detail sprays affecting wax?! They are actually beneficial as they add protection, so in effect top-up your wax. I highly recommend Bouncers Done & Dusted.
A quick note about your wheel sealant. Strip it and use the Collinite, it'll last longer than the Poorboys, or invest in some Finish Kare FK100P High Temp Paste Wax (you can use it on the whole car too), it was designed for aircraft originally and can withstand temps above 250c. It makes a brilliant wheel sealant.